The clinician should explain the procedural steps to the patient prior to machine entry and head positioning so the patient can anticipate what will happen next and not be alarmed by the mechanical function of the panoramic machine. The clinician should place the panoramic lead apron fully clearing the back of the neck region; high in front, low in back. Note that the panoramic lead apron has a poncho-type configuration different from lead shields used in intraoral radiography. The preferred panoramic lead (or lead-equivalent) apron has a front and back panel of the same length. If the panoramic lead apron has front and back panels of different length, it is best to place the long panel on the patient’s back and the short panel in the front because the x-ray beam enters from behind the patient’s head. Do Not Use a THYROID COLLAR. The use of a thyroid collar or improper lead apron placement will block the x-ray beam and prevent imaging of structures at or near the midline. The clinician must keep in mind that the x-ray beam enters from behind the patient’s head in a lingual to labial direction.
The purpose of the lead apron is to reduce the somatic exposure of radiosensitive tissues and minimize genetic exposure to the reproductive organs. In the head and neck region the most radiosensitive tissues are the thyroid and salivary glands and the hemopoetic tissues of the bone marrow located in the mandible and the sternum. Because of the nature of the panoramic exposure, both the salivary glands and mandible are irradiated; therefore the role of the lead apron is to provide maximum shielding of the remaining radiosensitive organs. In addition, it should be remembered that the x-ray beam is directed from behind the patient’s head and directed slightly upwards. Hence the greatest risk to these tissues is from scatter radiation.